The present invention relates to printing presses having shiftable cylinders and to a mechanism for shifting the positions of printing cylinders within a printing press.
There are known printing presses in which the position of a blanket cylinder may be changed to provide different modes of printing. Typically, these presses include an impression cylinder, a pair of blanket cylinders, and a pair of plate cylinders. The blanket cylinders are mounted so that they can be shifted between two positions. In a first position the blanket cylinders simultaneously print on opposite sides of a web passed between them. This mode is known as a perfecting mode. In a second position the blanket cylinders each cooperate with the same impression cylinder. When the press is set up in this mode, it will print two impressions, usually in different colors, on one side of a web. The plate cylinders are moved to effect a change in the printing mode.
Frequent jams of the web have been a problem with known web presses having a pair of shiftable blanket cylinders and a common impression cylinder. When such a press is in the perfecting mode, the rotating impression cylinder can catch the web, and once a jam has started, the impression cylinder forces the web backwards against the direction of rotation of a blanket cylinder. This makes a bad situation worse because the cusp between the blanket cylinders gets stuffed with web which is not easily removed.
This problem can be solved by increasing the distance between the blanket cylinders and the impression cylinder when the blanket cylinders are in the blanket-to-blanket perfecting mode. In the past this has been done by mounting the impression cylinder so that it can be moved upward away from the cusp defined by the blanket cylinders when the blanket cylinders are in the blanket to blanket, perfecting mode. This has been effective in eliminating the jamming problem, but other disadvantages have resulted.
It has been suggested to provide a press of the type discussed above with an additional printing couple having a blanket cylinder which bears against the common impression cylinder. In such a press it would be possible to print three colors on a single side of a web, or to print two colors on one side and one color on the other side of a web, or to print on two entirely different webs simultaneously. When such a press is equipped with an impression cylinder which is movable to reduce jamming, the third or upper deck blanket cylinder must be set to one side or the other of a vertical plane through the impression cylinder so that the upper deck blanket cylinder does not obstruct the path of movement of the impression cylinder. This requirement has given rise to presses having so-called left-handed or right-handed upper decks depending on which side of the vertical centerline of the press the upper deck blanket cylinder is located. Whether a particular user had a press built for him with a left-handed or right-handed upper deck depended on what web lead he was likely to want most often. With a left-handed upper deck some web leads are possible which are not possible with a right handed upper deck, and vice versa.
The selection of web leads is limited in part by the necessity of having an impression cylinder scrubber. The impression cylinder scrubber deposits a thin film of water on the impression cylinder to prevent the build-up of ink on its surface. When a left or right-handed upper deck is used, there is not room for a scrubber between the upper deck blanket cylinder and the closest lower deck blanket cylinder. The impression cylinder scrubber must be positioned on the side of the vertical plane through the impression cylinder opposite from the upper deck blanket cylinder. Because of this requirement, the impression cylinder scrubber further restricts the number and flexibility of web leads.
In addition to problems with jams and the upper deck blanket cylinder discussed above, known printing presses which have two modes of printing are not easily shifted between modes. The mechanisms utilized to shift the cylinder positions in printing presses having two printing modes vary. For example, U.S. Pat. Nos. 3,986,454 and 3,769,910 disclose offset web presses in which each blanket cylinder is pivotable about an axis coincident with the axis of the cooperating plate cylinders. Another cylinder shifting mechanism is shown in French Pat. No. 1,257,552. In this press each blanket cylinder is mounted in double eccentrics from each of which a lever extends. The levers in turn are connected by links and are moved simultaneously to shift each cylinder's position.
Other cylinder shifting mechanisms are shown in U.S. Pat. Nos. 3,452,672 and 3,329,086. In the presses disclosed in these patents cylinders are mounted in eccentric bushings and various links and levers connect hydraulic or pneumatic cylinders to the bushings and cause them to rotate to shift the cylinders' positions.
Presses of the type discussed also have throw-off mechanism to disengage the cylinders from each other for make ready. The throw-off mechanisms have generally been part of the cylinder shifting mechanism. In U.S. Pat. Nos. 3,452,672 and 3,329,086 the eccentrics which enable mode changing also are utilized for throwing off the cylinders. In both cases a linkage which shifts the cylinders' positions must be manually shifted or adjusted before modes of printing can be changed. In U.S. Pat. No. 3,452,672 a pneumatic or hydraulic cylinder is actuated to achieve throw-off; changing of printing modes is achieved by manually removing a pin, turning a gear and then reinserting the pin. In U.S. Pat. No. 3,329,086 a link (unnumbered and shown in the lower right of FIG. 2a) is connected by a pin to a linkage which controls throw-off and mode shifting. To shift modes the connecting pin is shifted from its upper position to its lower position by manually turning a threaded rod. From this review of the prior art it is clear that in the known presses which are capable of two modes of printing, shifting between modes has required manual manipulation of a control linkage.